JPL Scientists Used GPS to Find Total Weight of Winter Snowpack, Soil Moisture

Scientists utilized global positioning systems to find the total weight of winter snowpack and soil moisture in the Sierra Nevada region, potentially giving state resource managers a better estimate of  how much water is available to meet needs, the Jet Propulsion Laboratory announced today.

For the study, a JPL team reviewed data from 1,069 GPS sites in California, Nevada, Oregon and Washington, dating to 2006.

"For each site, they averaged the difference in the ground level between Oct. 1 -- the end of the dry season -- and April 1 of each year, when the snow is likely to be at its greatest weight," according to a JPL statement.

From that data, scientists calculated how much water is required to create the observed height changes.

Scientists say water weight causes the Earth to sag, analogous to the way a mattress sags under a sleeping person.

Like a mattress, the sagging from water is localized, "so that a heavy mountain snowfall depresses the ground beneath it but barely affects flatlands 40 to 50 miles away," the statement said. "GPS receivers accurately monitor the location and extent of the ground's sinking in winter and rebounding in spring."

JPL research scientist Donald Argus called the study groundbreaking.

"Researchers have known that up-and-down movements observed in GPS sites may be due to the weight of water, but this is the first time we've inferred the volume of water from GPS movements," Argus said.

The new data complements information obtained by NASA airborne and space missions that measure the water cycle.

The study recently was published in Geophysical Research Letters.

—City News Service